The present invention relates to a data receiving device, a semiconductor integrated circuit, and a method for controlling a data receiving device, and in particular, relates to a data receiving device, a semiconductor integrated circuit, and a method for controlling a data receiving device that can reduce power consumption.
There is a data transfer system using differential signals. This data transfer system using differential signals is used in a high-speed serial interface such as USB (Universal Serial Bus), HDMI (High-Definition Multimedia Interface), MIPI (Mobile Industry Processor Interface), and the like.
Japanese Unexamined Patent Publication No. Hei 11 (1999)-205412 (Patent Document 1) discloses a technique related to a USB controller capable of reducing power consumption. FIG. 13 is a diagram showing the configuration of the USB controller disclosed in Patent Document 1. The USB controller shown in FIG. 13 includes a Root_HUB 132 and an I/O buffer 133.
The Root_HUB 132 includes a port state circuit 151 and a port monitor circuit 161. The port state circuit 151 outputs a port status signal P_SUS by host software control. Whether or not data is being transferred through the use of the USB controller is managed by host software based on a signal from the port monitor circuit 161.
Registers 152 and 153 are configuration registers provided in the USB controller and can be accessed by a CPU. Irrespective of the port status signal P_SUS from the port state circuit 151, power-down control information for on/off control of a differential input buffer 159 is written to the register 153 by software. When power-down control information indicating the off control of the differential input buffer 159 is written to the register 153 by software, an output signal EMPD of the register 153 is set to “H”.
Selection information for selecting either on/off control of the differential input buffer 159 using the port status signal P_SUS from the port state circuit 151 or on/off control of the differential input buffer 159 using the power-down control information in the register 153 is written to the register 152 by software. When selection information indicating the selection of on/off control of the differential input buffer 159 using the port status signal P_SUS is written to the register 152, an output signal EAPD of the register 152 becomes “H”. Then, the port status signal P_SUS is outputted from the output of an AND gate 155, and supplied as a suspend signal SUSP through an OR gate 157 to the I/O buffer 133.
When selection information indicating the selection of on/off control of the differential input buffer 159 using the power-down control information in the register 153 is written to the register 152, the output signal EAPD of the register 152 becomes “L”. Then, an inverter 154 inverts the signal from “L” to “H”, which is supplied to one input of an AND gate 156. Therefore, the signal EMPD is outputted from the output of the AND gate 156, and supplied as the suspend signal SUSP through the OR gate 157 to the I/O buffer 133.
The suspend signal SUSP is used for operation control of output buffers 158a and 158b and the differential input buffer 159 in the I/O buffer 133. The logical OR by an OR circuit 160 between a transmission enable signal TXENB and the suspend signal SUSP is sent to the control terminals of the low-active output buffers 158a and 158b. Further, the suspend signal SUSP is directly sent to the control terminal of the low-active differential input buffer 159. The transmission enable signal TXENB is a signal which becomes “L” when the USB controller outputs data to a USB device. Reference symbol USBRCV denotes an output signal of the differential input buffer 159.
In the technique disclosed in Patent Document 1, the on/off control of the differential input buffer 159 in the USB controller using the Root_HUB 132 reduces the power consumption of the USB controller.
Japanese Unexamined Patent Publication No. 2006-135397 (Patent Document 2) discloses a technique for reducing the power consumption of a data transfer control device. Japanese Unexamined Patent Publication No. 2004-72225 (Patent Document 3) discloses a technique for reducing the power consumption of a USB controller.